The present invention relates generally to center pivot irrigation systems, and more particularly to center pivot irrigation systems which are adapted to selectively provide irrigation to substantial portions of corner regions.
Center pivot irrigation systems for irrigating large areas, such as agricultural areas, are now well known. For example, the model 2200 center pivot irrigation system, commercially marketed by Lockwood Corporation, Gering, Nebr., irrigates approximately 130 acres about a center using an elongated main pipeline sprinkler having a plurality of main fluid discharge nozzles which are spaced along the main pipeline. This system has proven to be advantageous for irrigating the inner acres of a rectangular plot. However, for the rectangular plot substantial areas in the corners are not irrigated by the center pivot sprinkler system. Accordingly, it is highly desirable to provide apparatus for adapting such a now conventional center pivot irrigation system into a system which additionally will irrigate much of the corner areas lying outside the generally circular area.
Various corner irrigating systems for use with center pivot irrigation systems have been proposed. One such proposal suggests the utilization of an electrically actuated water gun disposed on the end of the main pipeline sprinkler. Actuation of the end gun applied irrigation fluid from the main pipeline sprinkler to areas outside the main circular area. The end gun was to be actuated upon a particular orientation of the main pipeline sprinkler as a corner was approached, and was to be maintained in actuation until the main pipeline sprinkler swept past the corner. Although such a proposal may have been an improvement over systems without corner irrigation apparatus, it failed to account for the effect of the drain of the end gun on the rate of discharge of the main pipeline sprinkler. Furthermore, use of only a single end gun in the corner areas provided only a single level of improvement over the then existing systems, leaving substantial corner portions still unirrigated unless areas outside the corners also received irrigation.
Other proposals for irrigating corner sections have suggested the use of an auxiliary sprinkler system mounted on a controllably moving boom. The boom was pivotally connected to the distant end of the main pipeline sprinkler and carried auxiliary nozzles. In such proposals, the boom would pivot outwardly in the corner areas and the auxiliary sprinkler system would be actuated for irrigating the portions of the corner areas lying outside the inner circular area. These systems have either required a rather sophisticated drive mechanism which was programmed to cause the boom to swing in and swing out in the corner areas, and/or such systems required a buried conductor which served to guide the boom outwardly and inwardly in corner regions. The systems according to these proposals have not received full commercial acceptance and success because they have been relatively expensive and costly to service.
One of these proposed systems having such a boom type auxiliary sprinkler system suggested that, while advancing the auxiliary boom inwardly and outwardly, the pivotal rate of the main pipeline sprinkler should be reduced. This reduction in pivotal rate was to maintain sufficient water pressure supplied to the systems such that a special subsystem for regulating the rate of discharge from the various nozzles could be maintained operable and thus be utilized. This system did not recognize the advantages which could be achieved by operating the auxiliary sprinkler system only when the main pipeline sprinkler was neither pivoting nor providing irrigation fluid to the inner circular area.